To what degree do spatial and limnological predictors explain the occurrence of a submerged macrophyte species in lotic and semi-lotic/lentic environments of a dammed river?

Abstract

Insufficient knowledge about ecology of weed macrophytes from a large-scale perspective narrows the necessary decision-making for biodiversity conservation. The present study aimed to assess the occurrence frequency of Egeria densa in lotic and lentic/semi-lotic environments from a Brazilian dammed river, as well as to quantify the attributed explanation (pure or combined) by limnological and spatial variables on species occurrence frequency. Between 2006 and 2010, we repeatedly visited sample points classified as lotic (45) or lentic/semi-lotic environments (23) to collect data on species occurrence and limnological variables. We also generated spatial variables derived from latitude and longitude of sample points. E. densa showed a recurrent occurrence in the sample points classified as lentic/semi-lotic. Both spatial variables (16) and limnological variables (total phosphorus, nitrate, nitrite, transparency and turbidity) significantly contributed to explaining the species occurrence frequency. Forty-nine percent of the occurrence frequency variation was accounted purely by spatial variables. However, less than five percent of occurrence frequency variation was accounted purely by limnological variables. The several dams placed along the river determined the lentic/semi-lotic environments formation and regulated the dispersion processes of individuals of E. densa, consequently causing a recurrent occurrence of this species in particular environmental classes.